<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta http-equiv="X-UA-Compatible" content="IE=edge" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>Document</title>
    </head>
    <body>
        <div id="app">
            lastName:<input type="text"  v-model="lastName"/>
            firstName:<input type="text" v-model="firstName"/>
            fullName: <input type="text" v-model="fullName" />
        </div>
        <script src="../vue.js"></script>
        <script>
            new Vue({
                el: '#app',
                data() {
                    return {
                        firstName: '',
                        lastName: '',
                    };
                },
                computed: {
                    fullName(){
                        return `${this.lastName}${this.firstName}`;
                    }
                }
            });
        </script>
    </body>
</html>
